1. Field of the Invention
The present invention relates to a memory device which is comprised within an electronic computer or used for a terminal equipment of a computer, and more particularly to a memory device which is capable of preventing a trouble in missing of data being recorded on an information recording medium.
2. Description of the Prior Art
A variety of memory devices, which are capable of storing information by accumulating it in a recording medium by chemical, electrical, magnetical and mechanical means, have generally been proposed for the cases where such information is required to be stored. Particularly, since electronic computers have been introduced quickly in various technical fields in recent years, a memory device which records information magnetically or optically using a disk type information recording medium (hereinafter called a disk as required) is attracting attention of those who are skilled in such fields for storing computer programs and information such as results of operational processing.
An example of such a memory device has been disclosed in patent laid-open No. 60-101777 laid on June 5, 1985 by the Patent Office in Japan, "Hard Disk", "ELECTRONICS" p. 60-65, April, 1985, published by OHM Co., Ltd., and "Knowledge of Software" (Koji Yada, 1982), p. 75-85, published by OHM Co., Ltd. FIG. 1 illustrates a magnetic disk apparatus as an example of such memory device having the structure which schematically shows the outline of "positioning mechanism of magnetic head" reported by Japanese patent laid-open No. 60-101777. In this figure, a reference numeral 1 represents a support plate; 2, a rotary apparatus such as a spindle motor installed on the support plate 1; 3, a disk such as a magnetic disk as a recording medium loaded to a rotating shaft of the rotary apparatus 2; 4, a pressure spring of which one end is fixed to an arm 5 and the other end is provided with a head 6, for example, such as a record and read magnetic head with its surface located upward. 7 represents a support mechanism which supports the arm 5. 8 represents a rotation detector which detects rotation of a rotary apparatus 2 and therefore rotation of the disk 3 and outputs a rotary pulse signal. 9 represents a head transfer mechanism which comprises the support mechanism 7 and transfers the head 6 in the radius direction of disk 3 and 10, a head drive circuit which drives the head transfer mechanism 9. 11 represents a record and read circuit which outputs a record signal to the head 6 for writing information to the disk 3 or provides a read signal from the signal read from the disk 3 through the head 6 and 12 represents a disk drive circuit which drives the rotary apparatus 2.
13 represents a control apparatus which, for example, comprises a central processing unit, receives a rotary pulse signal as an input from the rotation detector 8, totally controls the head drive circuit 10, record and read circuit 11 and disk drive circuit 12, and also receives the information to be recorded on the disk 3 as an input and outputs the information read from the disk 3 in connection with a computer (not shown).
Operations of the structure of FIG. 1 are explained hereunder. While, the rotary apparatus 2 and disk 3 are not operated, the head 6 is pressured in contact with the recording surface of a disk 3 with an upward pressure of the pressure spring 4 which pressurizes the head 6.
When the rotary apparatus 2 is rotatably driven in the starting of the rotary apparatus 2 with the disk drive circuit 12 which has received the start command from the control apparatus 13, the disk 3 rotates, a downward floating force is generated to the head 6 by the viscous air flow generated on the surface of disk 3 and thereby the head 6 is gradually floated on the recording surface of disk 3.
Meanwhile, when the disk 3 rotates, a rotary pulse signal is output from the rotation detector 8. The control apparatus 13 controls rotation of rotary apparatus 2 through the disk drive circuit 12 in accordance with such rotary pulse signal, for example, to the constant value of 3600 r.p.m. Under the constant rotation of the rotary apparatus 2 and disk 3, the floating force is balanced with a pressure force of pressure spring 4 which pressurizes the head 6 and a small gap is maintained between the disk 3 and the head 6. Thereby, the head 6 is arranged opposed to the disk 3.
When a record or read command is sent to the record and read circuit 11 through the control apparatus 13 from a computer (not shown) under such condition, information is recorded to or read from the disk 3 through the head 6 by the control of the record and read circuit 11. Of course, in this case, the head transfer mechanism 9 which has received a drive command from the control apparatus 13 through the head drive circuit 10 in order to set the head 6 on the predetermined track on the disk 3 drives the support mechanism 7 in the radius direction of the disk 3. Next, during control of the rotary apparatus 2, when the drive stop command is applied to the disk drive circuit 12 from the control apparatus 13 and the rotary apparatus 2 is no longer driven by the disk drive circuit 12, rotating velocity of the rotary apparatus 2 and disk 3 is lowered by the control. Thereby, a floating force of head 6 becomes smaller than a pressure of the pressure spring 4, the head 6 gradually comes closer to the surface of disk 3 and rotation stops. As a result, the head 6 is placed again in contact with the recording surface of disk 3.
Since the memory apparatus of the prior art is formed as explained above, it has raised the problems that the head is indirectly or directly in contact with the disk when dust generated within the inside of memory apparatus flows through a very small gap between the head and disk or the memory apparatus receives an intensive vibration or impact from the outside. Accordingly, the head or disk is gradually damaged, the head cannot be floated from the disk after use over a long period of time and thereby the stored information on the disk is lost.
Such problems are generated because either the head or the disk or both of them are damaged and a friction resistance between them becomes large. When a friction resistance becomes large, the brake time becomes short or the start time becomes long due to the influence of such friction resistance when the rotating magnetic disk and rotary apparatus stop or when the magnetic disk and rotary apparatus start to rotate and thereby contact condition between the head and information recording surface of magnetic disk becomes longer. Therefore, it is important for preventing generation in the troubles of apparatus to detect that a friction resistance is increasing by detecting an interval between rotary pulse signals while the rotary apparatus is started or braked and to provide an adequate measure before it becomes impossible that the head be floated from the disk surface.